Axial piston motor

ABSTRACT

The invention relates to an axial piston motor ( 1 ), especially a compressor for the air conditioning system of a motor vehicle, comprising a housing ( 2 ) and a compressor unit ( 6 ). Said compressor unit is driven by a drive shaft ( 8 ), is arranged in the housing ( 2 ), and is provided for sucking and compressing a cooling medium. The compressor unit ( 6 ) comprises pistons ( 15 ) which move in a reciprocating motion in a cylinder block ( 18 ) and comprises a drive disc ( 11 ) which rotates with the drive shaft ( 8 ) and which drives the pistons ( 15 ). The aim of the invention is to obtain a delivery rate which is independent of rotational speed. To this end, the invention provides that the mass of the drive disc ( 11 ) is calculated such that the centrifugal forces generated when the drive disc ( 11 ) is rotating are large enough to counteract the pivoting movement of the drive disc ( 11 ) while actively regulating the same, and to influence the piston stroke and thus the delivery rate, especially to reduce or to limit the same.

[0001] The invention relates to an axial piston motor, in particular a compressor for the air conditioning system of an automobile, with a housing and a compressor unit arranged in the housing and driven via a drive shaft for taking in and compressing a refrigerant, the compressor unit comprising pistons reciprocating in the axial direction in a cylinder block and a drive disk corotating with the drive shaft and driving the pistons.

[0002] Axial piston motors or compressors of the kind under discussion are in most cases referred to as air conditioning compressors and are known from practice in a large variety of types. Compressors of this kind comprise a housing, which encloses an externally driven compressor or pump unit. The pump unit in turn, which is designed and constructed as an axial piston motor or axial piston pump, comprises at least one piston, which is adapted for reciprocal movement in a cylinder block. Normally, such a compressor is equipped with a plurality of pistons, which are axially reciprocated in the direction of their longitudinal axis during the movement of a swash plate via a receiving disk or during the pivoting movement of a pivot disk. In the case of a swash plate, the receiving disk is supported for corotation in the housing.

[0003] Swash plate compressors are known in a large variety of types, for example, from DE 44 41 721 A1 and DE 196 11 004 A1.

[0004] According to DE 44 41 721 A1, the compressor comprises a swash plate mounted on a drive shaft for purposes of performing a uniform rotational movement. The swash plate is coupled with a plurality of pistons that are adapted for reciprocal movement in a cylinder block. The cylinder-piston arrangement is used for compressing a gas. The pistons may also be double-acting pistons.

[0005] Concretely, the swash plate cooperates with the receiving disk that is joined to the piston. This receiving disk is arranged for corotation in the housing of the compressor, and supported via a support device in a cororational thrust bearing. The thrust bearing is used to absorb the torque that is transmitted from the rotating swash plate to the receiving disk.

[0006] Furthermore, in the case of the known axial piston motors or compressors of the kind under discussion, it is essential that the angle of inclination of the swash plate or pivot disk can be changed by means of a special joint mechanism for purposes of changing the piston stroke in the axial direction. Regardless of its concrete construction, this swash plate or pivot disk is hereafter always referred to as drive disk for the sake of simplicity. With respect to the longitudinal axis of respectively the piston or drive shaft, the drive disk tilts because of its geometric arrangement or because of the pivot axis there.

[0007] In particular for use in the air conditioning system of an automobile, it is necessary to keep the flow rate of the compressor, and thus its performance over the rotational speed range, at least largely constant to be able to ensure a constant performance of the air conditioning system. This requires a speed-independent flow rate of the compressor. To realize such a speed-independent flow rate, it is possible to realize a regulation in accordance with the state of the art known from practice. Accordingly, in the case of a rotational speed variation, the pressure in the drive chamber is changed via a control loop such that the flow rate is kept constant by changing the angle of the pivot disk and, thus, of the piston stroke by an active regulation. However, such a regulation is insofar disadvantageous as only a sluggish response characteristic is realizable in the case of a change in the rotational speed of the drive.

[0008] It is therefore an object of the present invention to improve and further develop a compressor of the described kind such that it is especially suitable for realizing a speed-independent flow rate.

[0009] The axial piston motor of the present invention accomplishes the foregoing object by the characterizing features of claim 1. Accordingly, an axial piston motor of the initially described kind is characterized in that the rotating mass of the drive disk or of the pivotable component of the drive disk is proportioned such that the centrifugal forces, which develop during the rotation of the drive disk, suffice to counteract the pivoting movement of the drive disk in a purposely regulating manner, and to influence therewith, in particular to lessen or limit the piston stroke and thus the flow rate.

[0010] To begin with, it has been recognized by the present invention that the centrifugal forces developing during the rotation of the drive disk result in that the drive disk tends to align itself with its axis of rotation parallel to the axis of the drive shaft, thereby reducing the pivoting angle. In the case of an adequate magnitude, this phenomenon leads to a reduction of the piston stroke, and that occurs automatically because of the developing centrifugal forces, which in turn result from the rotational movement of the drive disk.

[0011] Furthermore, it has been recognized in accordance with the invention that the corresponding, resetting pivoting torque of the drive disk increases in proportion to the square of the rotational speed, whereby, contrary to the previously discussed phenomenon, the piston stroke decreases—as the speed increases.

[0012] It has further been recognized that, due to their mass moment of inertia, the translationally moved masses (including the pistons) of the compressor unit tend to move beyond their respective dead centers. As a result, the translationally moved masses exert an inertial force or mass force and, thus, a pivoting torque, on the drive disk in the sense of a forced increase of the piston stroke.

[0013] Finally, it has been recognized that for realizing a speed-independent flow rate, one can make positive use of the foregoing phenomena in that one proportions the rotating mass of the drive disk such that the centrifugal forces, which develop during the rotation of the drive disk, suffice to adequately counteract the pivoting movement of the drive disk, and to influence therewith the piston stroke and, with that, the flow rate over the speed range, in particular to reduce or limit it at high rotational speeds. In accordance with the invention, a kind of balance of the centrifugal forces is produced against the force of the pivoting mass, which is caused by the translationally moved masses, in particular the pistons. The realization of the balance of centrifugal forces against the translational forces depends on the rotating mass of the drive disk.

[0014] Likewise, it is possible to proportion the rotating mass of the drive disk such that the centrifugal forces developing during the rotation of the drive disk and counteracting the pivoting movement of the drive disk, approximately compensate the forces, which the pistons exert on the drive disk, and which cause a more extensive pivoting movement of the drive disk. As a result, it is avoided that due to the force exerted by the pistons on the drive disk, an increase of the piston stroke occurs and, with that, an increase in the flow rate.

[0015] Furthermore, it is possible to proportion the rotating mass of the drive disk such that the centrifugal forces developing during the rotation of the drive disk and counteracting the pivoting movement of the drive disk, are higher than the forces exerted by the pistons on the drive disk and causing a more extensive pivoting movement. In this instance, there occurs not only a compensation, but also an overcompensation of these forces, whereby a flow rate is reduced, which is otherwise bound to increase along with the increasing speed of the drive shaft. Last but not least, there predominates in this instance the “tendency” of the drive disk to decrease the piston stroke beyond the state of equilibrium. Since the corresponding pivoting torque of the drive disk increases in proportion to the square of the rotational speed, the piston stroke decreases as the rotational speed increases, in the ideal case in such a manner that a constant—speed-independent—flow rate adjusts or results.

[0016] Concretely, it will be of advantage, when the mass of the drive disk is about 10% to 60% above the common mass of all pistons. Preferably, the mass of the drive disk is about 30% to 50% above the common mass of all pistons for purposes of attaining the previously discussed—automatic—regulation of the flow rate.

[0017] Furthermore, it should be remarked that the axial piston motor under discussion is an axial piston compressor of the swash-plate type or of the pivot-disk type. Accordingly, the rotating drive disk is constructed as a swash-plate or as a pivot disk. In the instance of the swash-plate construction, a corotational receiving disk mounted in facing relationship with the swash plate is arranged between the swash plate and the piston, the receiving disk biasing the pistons indirectly or directly, or effecting their axial movement.

[0018] There exist various possibilities of improving and further developing the teaching of the present invention in an advantageous manner. To this end, reference may be made on the one hand to the claims dependent from claim 1, on the other hand to the following detailed description of an embodiment of the invention with reference to the drawing. In conjunction with the description of the preferred embodiment of the invention with reference to the drawing, also generally preferred improvements and further developments of the teaching are explained.

[0019] In the drawing:

[0020] The only FIGURE is a schematic side view, partially cut, showing an embodiment of an axial piston motor according to the invention, the axial piston motor being an axial piston compressor of the swash-plate type.

[0021] The only FIGURE is an axially sectioned, schematic view of a compressor 1 for the air conditioning system of an automobile. The compressor 1 comprises a housing 2, which in turn consists of a first housing portion 3 and a second housing portion 4. The first housing portion 3 encloses a drive chamber 5, which accommodates a compressor unit 6. The compressor unit 6 is driven via a belt pulley 7 and via a drive shaft 8, which in turn is driven by an internal combustion engine of the automobile not shown in the FIGURE. The drive shaft 8 rotates about an axis of rotation 9.

[0022] In the housing 2, the drive shaft 8 is supported by means of a movable bearing 10 in the vicinity of belt pulley 7. A swash plate 11 is connected to drive shaft 8 not only for corotation therewith, but also for pivoting about same, so that the swash plate 11 rotates together with drive shaft 8. The swash plate 11 is secured against axial displacement, i.e., against a displacement in the direction of the axis of rotation 9.

[0023] Via bearings 12, the swash plate 11 acts upon a receiving disk 13 mounted for corotation in housing 2, and which connects via a connection rod 14 to each of pistons 15. During the rotation of swash plate 11, the pistons 15 are reciprocated via receiving disk 13 in the direction of the longitudinal axis 16 of pistons 15.

[0024] As can further be noted from the only FIGURE, the pistons 15 extend in bores 17, which are machined out of a cylinder block 18. The cylinder block 18 adjoins a valve disk 19, through which the medium having been compressed via compressor unit 6, is advanced into a pressure chamber 20 also named high pressure chamber. The pressure chamber 20 is formed in the second housing portion 4.

[0025] In accordance with the invention the rotating mass of the drive disk—here swash plate 11—is proportioned such that the centrifugal forces that develop during the rotation of the drive disk or swash plate 11, suffice to counteract at least slightly the pivoting movement of swash plate 11 (in this instance, the piston stroke is increased). This influences the stroke of pistons 15 and, thus, the flow rate as a function of the mass of swash plate 11. In other words, a regulation is realized as a function of the mass of swash plate 11.

[0026] Based on the regulation mechanism as claimed by the present invention, it is now of very great importance that one can increase the rotating mass of swash plate 11 beyond the “state of equilibrium,” i.e., to such an extent that the “tendency” of swash plate 11 to reduce the stroke of piston 15 predominates. Since the corresponding pivoting moment of swash plate 11 increases in proportion to the square of the rotational speed, the stroke of piston 15 decreases as the rotational speed increases, so that in the ideal case a more or less constant flow rate results—over the entire speed range—without having to take further costly measures for changing the pressure in the drive chamber or for varying the pivoting angle of swash plate 11.

[0027] For purposes of avoiding repetitions, the general part of the specification is herewith incorporated by reference.

[0028] Finally, it should be emphasized that the foregoing, merely exemplary embodiment explains only the teaching of the present invention, without however limiting it to the embodiment. Combinations of characteristic features as have been selected both in the introduction of the specification and in the description of the FIGURE, are not mandatory. 

1. Axial piston motor (1), in particular compressor for the air conditioning system of an automobile, with a housing (2) and a compressor unit (6) arranged in the housing (2) and driven via a drive shaft (8) for taking in and compressing a refrigerant, the compressor (6) unit comprising pistons (15) axially reciprocating in a cylinder block (18) and a drive disk (11) driving the pistons (15) and corotating with the drive shaft (8), characterized in that the rotating mass of the drive disk (11) or the pivotable part of the drive disk (11) is proportioned such that the centrifugal forces developing during the rotation of the drive disk (11) suffice to counteract the pivoting movement of the drive disk (11) in a purposely regulating manner and to influence therewith, in particular decrease or limit the piston stroke and thus the flow rate.
 2. Axial piston motor of claim 1, characterized in that the rotating mass of the drive disk (11) is proportioned such that the centrifugal forces developing during the rotation of the drive disk (11) and counteracting the pivoting movement of the drive disk (11) approximately compensate the forces exerted by the pistons (15) on the drive disk (11) and causing a more extensive pivoting movement of the drive disk (11).
 3. Axial piston motor of claim 1, characterized in that the rotating mass of the drive disk (11) is proportioned such that the centrifugal forces developing during the rotation of the drive disk (11) and counteracting the pivoting movement of the drive disk (11) are above the forces exerted by the pistons (15) on the drive disk (11) and causing a more extensive pivoting movement.
 4. Axial piston motor of claim 3, characterized in that the rotating mass of the drive disk (11) is proportioned such that the centrifugal forces developing during the rotation of the drive disk (11) and counteracting the pivoting movement of the drive disk (11) are above the forces exerted by the pistons (15) on the drive disk (11) and causing a more extensive pivoting movement, so that the piston stroke decreases as the rotational speed increases by such an extent that a constant flow rate adjusts itself.
 5. Axial piston motor of one of claims 1-4, characterized in that the rotational mass of the drive disk (11) is greater than the sum of all translationally moved masses.
 6. Axial piston motor of claim 5, characterized in that the rotating mass of the drive disk (11) is about 10% to 60% above all translationally moved masses, in particular above the common mass of all pistons (15).
 7. Axial piston motor of claim 6, characterized in that the mass of the drive disk (11) is about 30% to 60% above all translationally moved masses, in particular above the common mass of all pistons (15).
 8. Axial piston motor of one of claims 1-7, characterized in that the rotating drive disk is designed and constructed as a swash plate (11), and that a receiving disk (13) supported for corotation and in facing relationship with the swash plate (11) is arranged between the swash plate (11) and pistons (15). 